Reduction of oxides



Dec. 22, 1953 H. E. TscHoP ETAL 2,663,631

REDUCTION OF OXIDES Filed Aug. 27, 1949 6 Sheets-Sheet 1 DeC 22, 1953 H.E. TscHoP ETAL 2,663,631

' REDUCTION( oF oxIDEs FiledrAug. 27, 1949 `e sheets-sheet 2 //1/ WA/MMRmaf-f2.5

Dec. 22, 1953 H E. TscHoP ETAL 2,663,531

REDUCTION OF OXIDES Filed Aug. 27, 1949 e sheets-sheet s WCLQM ATTORNEYDec. 22, 1953 H. E. rsa1-10F x-:TAL

REDUCTION OF OXIDES Filed Mig. 27. 1949 6 Sheets-Sheet 4 Dec. 22, 1953 lH. E. TscHo ET AL 2,663,631

REDUCTION OF' OXIDES Filed Aug. 27. V194,9 e sheets-sheet 5 CH3/WEER 665/l 4 l pff/5959i //////l/ Dec. 22, 1953 H. E'. TscHoP ET AL 2,663,631

REDUCTION oF oxInEs Filed Aug. 27, 194e csy Smets-sheet e Y cf/vrE/50i/YER aas Exam/s7- Mmm/v01. was-#53mm Patented Dec. 22, 1953 UNITED'ST'EES REDUCTON OF OXIDES Ware Application August V27, 1949, Serial No.112,774

12 Claims.

The present invention relates generally to an improved process fortreating raw oxidic materials containing nickel and/or vcopper to obtaintherefrom yhigh-'duality metal. More Vparticularly, the presentinvention relates to an improved process for partially reducing rawnickel and nickel-copper oxides to obtain a uniformly high metal contentin said oxides and then to subsequently directly smelt 'and renne saidpartially-reduced oxides to produce nished nickel and nickel alloyscontaining copper whereby the production of metal from said oxides isgreatly simpliiied and facilitated, to 1a machine having a n'ovelstructure for obtaining controlled partial reduction of said oxides, andto a unique partially-reduced oxide product.

Heretofore, the nickel and nickel-copper bessemer mattes and/or-sintered mattes available as raw material for the usual open-hearthfurnace, electric-arc furnace, or inductionfurnace smelting and reningprocesses were treated rst by roasting the nickel and/ orcoppercontaining mattes to oxides and then by partially reducing the hotoxides with charcoal in an endeavor to obtain a consistently uniform andsubstantially high metal content in said oxides. In some cases, a doubleroasting was necessary to obtain a lsatisfactoryelimination of sulfurprior to reducing with charcoal. The reduced nickel or nickel-copperoxides were then used as part of the smelting charge along with charcoalor tar coke in acid open-hearth melting and refining operations. Furtherprocessing included either direct casting into pigs or else duplexrefining the molten metal from the open hearth in a basic electric-arcfurnace before casting into ingots.

Another method of sulfur elimination in the matte-sintering process wasdeveloped whereby low-sulfur, raw nickel oxide or nickel-copper oxidescontaining essentially no free metal were produced, these oxides then`being smelted with tar-coke additions to molten metal in gas-nred,batch-type furnaces without preliminary roasting. This method was alsounsatisfactory in that reducing gases formed within the charge werediluted with and rapidly removed by the combustion gases. In addition,the coke-oxide mixture was insulating in character and heat penetratedvery slowly to the interior portions of the charge. The overall resultwas a relatively slow reaction which began on the exposed surface of thecharge and which proceeded slowly inwardly as the surface layers werereduced and melted away. Furthermore, contaminating ele- 2 ments, 'suchas sulfur, were introduced into the metal by the tar coke and had 'to beeliminated by subsequent desulfurizing treatments.

IThe art has long sought a simple, inexpensive method for rapidlyreducing oxides to obtain products of controlled composition which couldthen be directly converted to high-quality metal in a singlesmeltingererlning operation. '.Ihis problem was not solved |by any -ofthe conventional processes employed by or known to the art until theadvent of the present discovery. @ne phase of the problem of reducingthe oxides involves obtaining a high concentration of reducing gases incontact with the oxides which is necessary for rapid reduction of theoxides. This condition is attained only when dilution and contaminationof the reducing gases by nitrogen and/ or combustion gases is avoided.In actual practice, this condition cannot be `attained Vin a blastfurnace, a reverberatory-type furnace or la direct--red rotary kiln.Another phase of the oxide-reduction problem involves high thermalefficiency and excellent heat-transfer characteristics coupled with theemployment of inexpensive fuel. lThe numerous processes which have beenemployed and which were intended to produce high concentrations ofuncontaminated reducing gases in intimate contact with the oxides to bereduced have all been very unsatisfactory from the viewpoint of thermalefficiency, heat transfer and economy. .In particular, the conventionalmethods for producing nickel or nickel-copper alloys from the oxides ofthese metals have been relatively complicated, time 'and space consumingand costly. Furthermore, the metal content of the oxides reduced by theprior art methods preparatory to smelting and refining was variable andunpredictable.

Up to the Vpresent time, the art has failed to develop a technicallyefficient 'and economic process and apparatus which would obtainconccinitantly all the foregoing necessary conditions and satisfactorilysolve the problem in a practical manner, particularly on an industrialscale to produce commercially acceptable products. The Aforegoingremarks are especially applicable to the nickel industry where theVolumes of materials handled are less than are those handled in the ironand steel industry and where the metallurgical properties of the nickeland nickel-copper oxides, such as sulfur absorption, etc., differgreatly from those of iron and iron oxides. The pressing nature of theproblem is attested by the continued experimentation of the Bureau ofMines en oxide reduction processes 3 which likewise clearly indicatesthat the problem exists and that it has not yet been satisfactorilysolved by others skilled in the art.

It is an object of the present invention to provide a novel process forsimply, economically and rapidly producing nickel and nickel-copperalloys from raw oxides containing these metals which comprises asessential features in novel combination a unique operation for obtainingpartially-reduced oxides of uniform and consistently high metal content,directly converting said reduced oxides to high-quality metal in asingle smelting and refining operation without substantial addition ofsupplementary reducing agents.

It is another object of the present invention to provide as an essentialfeature in a novel combination of operations, an operation for obtaininga high degree of controlled partial reduction of nickel andnickel-copper oxides to obtain a product having consistently high anduniform metal contents and containing controlled amounts ofhighly-active carbon iinely dispersed throughout the partially-reducedoxides.

It is a further object of the present invention to provide as anessential feature thereof, a novel operation and a unique, easilycontrollable, unitary apparatus for producing partially-reduced oxidesof controlled composition from raw oxides which utilize relativelyinexpensive hydrocarbon gas, such as natural gas, to reduce said oxidesWith markedly low consumption of said gas by simultaneously combininghigh thermal efliciency together with high concentrations ofuncontaminated reducing gas in contact with the oxides.

The present invention also provides as an important but not essentialfeature the recovery and recirculation of valuable reducing componentsfrom the spent exhaust gas produced in the essential oxide-reductionoperation.

It is a further object of the present invention to provide unique,partially-reduced oxide products having uniform and consistently highmetal contents and controlled carbon contents.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the drawings, inwhich:

Fig. 1 gives, for purposes of comparison, flowsheet A illustrating aprior art process for producing nickel-copper alloy ingots and now-sheetB illustrating the much more simple and economic procedure for obtainingthe same results by the present novel process and apparatus;

Fig. 2 schematically depicts in perspective the location andtemperatures of the various zones in an annular oxide-reduction muiileembodying the novel structure of apparatus encompassed by the presentinvention. It is to be appreciated, however, that divisions between thevarious zones and the various temperature ranges are of necessityarbitrarily shown in Fig. 2 and that in actual operation said divisionsare not sharp but tend to blend into each other at the junctions betweenadjacent zones;

Figs. 3 and 4 are reproductions of macrophotographs at l0 magnicationsof two nickel-copper oxide particles, each partially reduced by one ofthe two embodiments of the essential oxide-reduction operation of thepresent process. The oxide particle shown in Fig. 3 was partiallyreduced by employing con-current gas flow and contains only about 9.05%carbon whereas the oxide particle shown in Fig. 4 was partially reducedby employing counter-current gas flow and contains about 3.85% carbon;

Fig. 5 shows a flow-sheet depicting one particular manner of combiningthe various operations, units of equipment and features of the presentinvention and, in addition, also includes the optional embodiment in theoxide-reduction operation of recirculation of reducing gases recoveredfrom spent exhaust gases;

Fig. 6 illustrates an elevational view, partly in section, on an annularoxide-reduction muiile which is a preferred embodiment of the presentinvention; and

Fig. 7 is a detailed'section of the annular muffle structure illustratedin Fig. 6.

Generally speaking, the present invention comprises a novel combinationof operations involving the rapid, controlled, partial reduction of rawoxides in a special oxide-reduction muiile of novel structure to produceunique partially-reduced oxide products having consistently high anduniform metal contents and controlled contents of finely-dispersed,highly-active carbon which are then directly convertedinto high-qualitymetal products by electric or induction-furnace practice withoutsubstantial additions of supplementary reducing agents.

Partially-reduced oxides treated by the present novel process aredirectly melted along with scrap by the usual electric-arc furnace orinductionfurnace technique, the conventional practice of preliminarymelting in an acid open-hearth furnace, desulfurizing, etc., prior toduplexing the melt in an electric furnace, being omitted. The purpose ofconventional preliminary open-hearth smelting prior to refining andfinishing in electric furnaces is necessary mainly to obtain a productsuitable for electric-furnace refining since oxides reduced byconventional methods have relatively low and Variable total metalcontents which render these oxides unsuitable for directelectric-furance smelting and refining.f

In order to obtain material suitable for electric-furnace refining, itis necessary that the oxides charged into the electric furnace behighgrade, i. e., of uniformly high total metal content, both from theviewpoint of metallurgical quality and also cost. The quality of reducedoxides produced by the prior art methods is not only relatively lowerfrom the viewpoint of total metal content but also is quite variable inmetal content, e. g., the variation usually is from about 767Lto about85% whereas the minimum desirable metal content for directelectric-furnace smelting is :at least about 88% total metal content.These factors render preliminary openhearth melting a necessaryoperation before electric-furnace rening and deoxidation can beeconomically and metallurgically feasible. On the other hand, thepartially-reduced oxides produced by the present novel process are ofsufficiently high and uniform in quality to permit direct smelting,refining and deoxidation by electric-furnace or induction-furnacepractice with considerable savings in operating, labor and equipmentcosts.

In order to clearly demcnstate the marked distinctions and advantages ofthe present process over conventional processes, two i'owsheets arepresented in Fig. 1. Flow sheet A shows a typical prior art process andow sheet B illustrates the much more efficient, simple and economicprocess embodying the present invention. in l. ilow sheet A shows theconventional operations for producing cast ingots containing about 76%nickel and 30% copper, such as sold under the trade-mark MoneL fromsintered nickel-copper oxide. Flow sheet ,B illustrates the presentimproved process. Identical amounts of scrap and oxide are shownentering each 'system and 100,000 pounds of the aforesaid nickel-'copperalloy as -ingots are produced by both systems. The advantages ef thepresent novel process as compared to the production syst-ern employingthe Old DlaCliQe ale readily lpalel by Comparing the tvo now sheets. Inthe latter, a small amount 'of tar coke and oxide Vis placed in thebottl'l Of Ythe electric furnace, mixed With SCT-2p, melted, refined andcast into ingots which comprise approximately 66% of the total tonnageproduced. The balance or the oxide is mixed with about 12% tar coke byweight and charged into a gasered, open-hearth furnace Where it isreduced and melted. The reduction and melting operation in theopen-hearth furnace is slow and inefficient since the oxideecoke mixturehas very poor heat-transfer characteristics. Reduction with Subsequentmelting occurs only on `the surface of the charge and any reducinggases, e. g., carbon monoxide, formed by the reaction of the coke withthe oxide are rapidly diluted with 'combustion gases and swept out ofthe furnace, thereby slowing the reducing action and wasting valuablereducing gases. Unreiined molten metal tapped from the open-hearthfurnace is de's'ulfurized in the ladle and the sulfur-containingimpurities are removed with the slag. De 'sulfurizatiton is necessarydue to sulfur pick-up from the coke which has been added to the oxidei'n the open-hearth furnace. This product is transferred to an electricfurnace for further refi'nn'g and is then cast into ingots.

In procedures employing the present new process, including the noveloxide-reduction operation, the oxide is partially vreduced in the noveloxide-reducing muilie employing counter-current gas now. Thepartially-reduced oxide containing a uniform high total metal contentand a controlled Vcarbon content is charged directly into the electricfurnace, melted, refined and cast into in'gots. A very small amount oftar coke, e. g., up to about 1,000 pounds of tar coke, may be added ifdesired together with the partially-reduced oxide. In this particularcase the optimum total metal content in the partially-reduced oxide isabout 91% copper plus nickel together with about 1.5% of carbon finelydispersed throughout the reduced oxide particles.

In the present process, both the conventional mixing and theladle-destilfurlaing operations have been eliminated. Furthermore, theduplexing operation, i. e., the combi-nation of openhearth andelectric-furnace operations, has been eliminated, thereby completelyavoiding all delays caused by the unequal tap-to-tap times for the 'twodifierent types of furnaces. Since the oxide partially reduced by thenovel oxide-reduction operation is discharged from the 'mule with alow-heat content, it can be stored normally and is available for directcharging into the electric furnace at any time without suiering any lossof activity of the contained, deposited carbon. Furthermore, any extracarbon additions (tar coke additions) made in the new system amount tonot more than about 15% of the tar colte added during processing by theold system, but even here this small amount of tar coke can beelimina-ted when employing the new process. Since the tar-cokerequirement of the new' process is either nil or at the most negligible,the problem of sulur contamination by tar coke is also negligible. Astill further advantage of the new process `is the fact that the ratioof scrap to partially-reduced oxide in direct electric-furnace smeltingcan be varied at will over a much Wider range than when processing byconvention-'a1 methods.

The physical properties and the metallurgical quality of the metals andalloys obtained as commercial products as a result of utilizing theprocess of the present invention is, in every Way, comparable to thequality of the metals and alloys obtained by the more costly and morecomplicated conventional duplex smelting and rening operations.

The novel oxide-reduction operation in the present process employshydrocarbon gas, e. g., natural gas, tc obtain the desired high degreeof controlled partial reduction or" the raw oxides. It is contemplatedthat the flow of the gases can either be con-current with orcounter-current to the feed of oxide through the reduction mullle,depending on the carbon content desired lin 'the 'final product. It hasbeen discovered that natural raw gas, e. g., a gas containing generallyabout to about 95% methane, is particularly applicable in the presentprocess.

In an embodiment of the oxide-reduction op eration, the relatively cool,raw, natural gas enters the novel reduction munie through the port fromwhich the partially-reduced oxide is discharged where it aids in coolingsaid oxide. As the gas flows counter-currently to the downwardly-movingcolumn of oxide and upwardly into the hightemperature reducing zone, theprogressively increasing temperature encountered accelerates thereduction reactions. The novel result is a partially-reduced oxide ofhigh, consistently uniform metal content discharging from one end of theapparatus and exhaust gases` resulting from the partial oxidation ofnatural gas and containing hydrogen, carbon monoxide, water vapor,carbon dioxide, nitrogen, hydrocarbon gases, etc., discharging from theother end of said apparatus.

The various zones and temperatures occuring within the reduction muniewhen employing counter-current gas flow to obtain partially-reducedoxides oi controlled composition are schematically illustrated in Fig.2. The cool raw natural 'gas I0, upon entering the oxide-discharge portof the reduction apparatus and upon coming into contact with reducedoxide Il in cooling zone I2, cools said oxide and is in turn preheated.Above the cooling zone, in zone I3, temperatures above about l000 F., e.g., at 'about 1l00 F. and higher, are obtained and some oxide reductionalso continues to take place to some extent in this zone. Carbon isprecipitated on and dispersed Within the particles of partially-reducedoxide and the remaining gas flows upwardly yinto regions ofprogressively increasing temperature containing progressively lessreduced oxide while, at the same time, continuously reacting with theunreduced oxide in main reducing zone Iii and in primary reducing Zonel5. The carbon which is deposited on the partially-reduced oxide iscarried downward with said oxide and, being intimately dispersed on andwithin the oxide particles f see Fig. e), provides a most excellent,highly-active, reducing agent for the subsequent electric-arc orvinduction-hlrnace direct sin-citing of the reduced oxide, operation le,to produce metal 10a.

The major function of primary reducing zone l5 is to complete thepreheating of the oxide to the reduction temperature range, e. g., about1790 F. to about W F., both by heat vsupplied by the intern-a1 andexternal heating chambers (see Figs.

6 and '7) of the novel annular mulile and also by absorption ci heatfrom the hot gases progressing upwardly through the oxide bed. lI'hesecondary function of zone le is to initiate the reduction of the oxidesince the gases leaving the reducing zone lai still possess potentialreducing power.

initial preheating of the entering raw oxide I8 occurs in the zone l@which is located immediately above the primary reducing zone but whichis positioned outside the external heating cham `er oi the muiile (notshown in Fig. 2) Preheating in Zone it is accomplished mainly by theheat absorbed from the large volurne of exhaust gases.

Heat is supplied to zones i2 to l5 by an external heating cham-ber 3e(Fig. 6), for muille diameters over about 5 inches by an internal(core-heating) chamber '2l (Fig. 7), and by the exothermicoxide-reducing reactions. In the present oxide-reduction operation, moregas is employed than is theoretically necessary to reduce the oxide tothe desired degree of partialreduction resulting in. an overall negativeheat balance. Good heat-transfer characteristics in the novel mullle aretherefore a necessary feature in obtaining the excellent results ci thepresent process. Excellent heat-transfer characteristics are attainedwithout unduly high temperature gradients in muilles or diameters inexcess of 5 inches by employing not only an external 'ieating chamberbut also an internal or coreheating chamber. in employingcounter-current gas flow, the Aupward-moving hot gases serve touniformly and gradually pre-heat the downwardmoving oxide and the heatis then returned to the incoming gases by the downward movement oi theoxide. The eliiciency of heat recovery is indicated by the fact that thetemperature oi the spent, exhaust gases il' (Fig. 2) is generally belowabout 220 F. Oxide pre-heating is not only desirable from the viewpointof returning otherwise wasted heat to the si stem but is also desirablefrom the viewpoint of uniform and gradual preheating of the incomingoxides to gether with initial reduction of said oxides by gases nowhaving only a relatively small reducing potential. This condition servesto prevent excessive rates of reduction. Excess reduction rates,obtained when raw oxide is quicklyexposed to hot, highly-reducing gasesmay cause sintering or fusion of the reduced oxide which, in turn, wouldpromote bridging in the muile, thereby preventing or hindering iiow ofthe oxide through the mufle.

The final, partially-reduced oxide product containing finely-dispersed,highly-active carbon has been found to be eminently suitable forsubsequent direct melting and rening. Partially reducing, rather thancompletely reducing, the 0xide together with deposition of carbon in thepartially-reduced oxide particles permits a much higher production or"throughput rate for any given size of reduction mullle than can berealized if the oxide is completely reduced and also permits equallyrapid conversion to metal in the subsequent melting and refiningoperations,

Cooling the partially-reduced oxide to at least about 550o F. 0r loweris not diilcult when employing the foregoing particular embodiment ofthe present process, namely, counter-current ow of gas to oxide. Heatabsorbed by the endothermic decomposition of the incoming gas cools theoxide to about 1100 F. with great rapidity. Further heat is absorbed inheating the cool incoming gas up to its decomposition temperature sothat the remaining amount of cooling to the required oxide-dischargetemperature is relatively small.

As disclosed hereinbefore, the partially-reduced oxide produced byemploying counter-current flow of gas to oxide contains finely-dispersedcarbon which can be controlled over a wide range by varying theoperational factors. The carbon content can be controlled between about0.4% and about 4.0% by Weight. Certain overall processing requirements,however, may make it desirable to produce partially-reduced oxidecontaining carbon in amounts lower than about 0.6 The aforesaidlow-carbon reduced oxide is produced by employing con-current flow ofgas with oxide wherein more of the carbon deposited on and within theoxide particles is oxidized to carbon monoxide or carbon dioxide than isthe case when counter-current gas ilow is employed. 1n this embodimentof the present process, the gas is introduced at the top of the muiilealong with the raw oxide and withdrawn at the bottom along with thereduced oxide. The carbon deposits on the oxide particles in the upperpart of the main reducing zone and most of the carbon thus depositedoxidizes as it passes downward with the oxide through the balance of themain reducing Zone. Carbon content of oxides reduced by this embodimentcan be held at values even below about 0.10% by this method, e. g., atabout 0.05% or even lower. However, the thermal efficiency of thisembodiment of the novel reduction operation is somewhat lower-than whenemploying counter-current gas flow because in counter-current :dow theheat of the exhaust gases is almost completely transferred to the coldraw oxide entering the Inutile. With con-current ow this heat is lost.Furthermore, with counter-current ilow the heat of the hot reducedmaterial is largely used to heat the incoming gas. With con-current flowthis heat is lost. In addition to the heat losses, Cooling of thereduced material to 'below its reoxidation temperature in air, e. g.,below about 550 F., becomes more difcult when employing con-currentflow; and for large furnaces the extension of the annular muffle intothe cooling zone from the reducing Zone becomes a matter of practicalnecessity.

For producing partially-reduced oxides most economically for directmelting and reiining by electric-furnace practice, it is preferred toemploy counter-current flow of gas to oxide because the degree ofreduction can be best controlled and carbon is deposited on andprecipitated within the iinal product particles in amounts between about0.i% and about 4%, preferably between about 1.0% and about 2.0% and morepreferably in an amount about 1.5% by weight of the nal product. Oxidepartially-reduced by concurrent gas low and containing carbon in amountsbelow about 0.6% usually is not as suitable for direct electric-furnacemelting as is oxide reduced by counter-current gas ilow and havinghigher carbon contents. However, under certain circumstances low-carbonpartially-reduced oxide may be required, in which case con-current flowof gas with oxide would be the most feasible embodiment of theoxide-reduction operation to employ. However, by proper control of theoperational factors of either embodiment, it is possible to secure auniform and high degree of reduction together with deposition ofcontrolled amounts of highly-active carbon finely dispersed within thepartially-reduced oxide particles which will promote rapid and completemelting and reinch of heating surface to 1.0 cubic inch of annularvolume. In an annular muiile, the ratio of mule heating area to muiiievolume is determined by the width of the annular space, indicated by theletter W in Figs. 2 and '7. For example, 6 O, D. 2" I. D., 14 O. D. l0"I. D., and O. D. l6 I. D. muiiies all have an annular Width, or width ofoxide bed, of 2 inches and each mufle has a surface area to volume ratioof 1,0. In the art it is well known that the terms O. D. and I. D. meansoutside diameter and inside diameter, respectively. Similarly, if thewidth W of the annular space is 3 inches, the aforementioned ratio willbe 0.6'7, and if the width is 4 inches, the ratio will be 0.50, etc.Thus, while both heating area and oxide-bed thickness are of primaryimportance in securing rapid heating of the oxide within the novelannular muflle, both factors may be expressed in terms of the width ofthe oxide bed. Thus, reducing the width of the annular space decreasesthe time required to heat the oxide to the desired temperature forreduction.

Another factor which is important in improving heat transferv and whichis influenced by the width of the annular space is the velocity of thereducing gas. For example, two tests, i. e., test Nos. 3 and 4, wereconducted in two different circular mufes, neither of which contained aninternal or core-heating chamber and in which the temperature of theoxide feeding through' the mules was measured at a point on the axis ofthe mufiie near the bottom of Zone i3 both before and after the reducinggas was introduced in counter-current flow to the movement of the Thevery considerable effect of rate of gas flow on heat transfer byconvection heating can be clearly seen in each of the above tests. Thereduction reactions begin as soon as the gas is turned on and the netheat balance is endothermic when there is an excess input of naturalgas, as was the case with the tests shown in Table II. Therefore, theincreases in temperature obtained by iiowing natural gas through themuflie, as illustrated by the foregoing test data, cannot be attributedto heat released by the reduction reaction since the net heat balance inthe system is negative, but must be attributed to the important effectof velocity of gas 110W through the muiiie. The relative gas velocity inan annular mufle is determined by the width of the annular space and bythe height of the reducing zone. In other words, the dimensions of themuflie tube have a very important effect on the eiciency of heattransfer in the muilie. Thus, for any given volume of gas input, theshorter the distance between inside and outside walls of the annularreduction chamber, then the higher the ratio of heating surface area tomufile volume, the shorter the width of the oxide bed through which heatmust be transferred, and the greater the velocity of the gas flowingthrough the oxide bed.

Circular, non-annular muflies having an inside diameter in excess ofabout 5 inches result in heat-transfer characteristics too poor tojustify economic commercial operation. The present, novel, annularmuflie overcomes this handicap and permits the construction of anydesired size of reduction furnace without loss of high heattransfercharacteristics. The width of the an-I nular muflie space (W in Fig. 2)is important from the commercial viewpoint and, for economic op eration,this width should not exceed about 5 inches and preferably not exceedabout 4 inches, particularly when nickel or nickel-copper oxides are tobe treated.

The balance of the test data disclosed in the present specification wasobtained in or pertains to one of three furnaces, the dimensions andoperating data for which are given in Table III. Test Nos. 15 to 26 and39 to 48, inclusive, were made in a small-scale, non-annular furnace(furnace A), and test Nos. 11 to 14 and 27 to 38, inclusive, were madein a medium-sized, semicommercial annular furnace (furnace B). Test Nos.5 to 10, inclusive, were computed for a largescale furnace of thedimensions of furnace C with the exception that the annular width wasvaried Y Table III Furnace Reduction Zone Data A B C Reducing Zone O.D., inches 3 G 18 Reducing Zone I. D., inches. 0 2 12 Reducing ZoneHeight, inches 30 63 135 Width of O xide Bed, inches. 3 2.0 3. 0 www 1.33 1. 00 o. 666

Volume Relative Reducing Gas Vclocities 1 2. 46 3. 75 Oxide Feed Rate,lbs/hr 40 350 3, 000 Reducing Gas Consumption in t 3/lb Oxide 1. 50 l.50 1. 50 Time in Reducing Zone, min 34. 5 29. 4 41. 3 Time at ReducingTemp., min. 17. 6 14. 4 17. l Reducing Temp., F 1, 700 l, 900 1,900

Since the reduction mufle of furnace A was only 3 inches in diameter(the width of the oxide bed), it was not necessary to provide thisfurnace with an internal, core-heating chamber. In this case, the highheating surface to mufile volume ratio, narrow width of oxide bed and arelatively high reducing gas velocity for this ratio and width resultsin good performance without core heating. In larger furnaces, highefficiency is obtained by employing core-heating means. The foregoingmuiiles obtain markedly improved results in that there is obtainedmaximum throughput capacity coupled with unusual and markedly superiorheat-transfer characteristics. Another factor controlling the width ofthe annular muiile space that can be employed is the particle size ofthe oxide charged, as discussed hereinafter. However, it has beendiscovered that there is an optimum width of annular mufle space foreach specic application of this novel reduction operation and that thiswidth is highly important from the viewpoint of economic practicability.For example, a certain copper-nickel oxide charged into furnace C at arate of 3000 lbs. per hour will require about 24.2 minutes to reach atemperature of about 1500o F. plus an additional time of about 16minutes at temperatures between about 1500 F. and about 1900 F. to bereduced about The data given in following Table IV were computed for afurnace having the overall; dimension of furnace C but with the annularwidth varied, calculations being based on data obtained on furnace B.These data illustrate the effect of varying the width ofthe annularmuille space on the time at temperature at a feed rate of 3000 lbs. perhour of oxide in all cases.

From the foregoing data, it may b e seen that when the factor of time atreducing temperature is introduced, the commercially practical opti--mum width of the annular space is not necessarily the minimum width. Forexample, use f av l-inch width results in very rapid heating (excellentheat transfer), but the volume of the muiile so reduced that the totaltime in the heating zone is less than the 16 minutes required to obtainabout 75% reduction. At the lother extreme, increasing the width of theannular space above about inches results in such poor heat transfer thatthe oxide never reaches the desired reduction temperature unless theoxide feed rate is lowered below a commercially acceptable rate. Fromthe foregoing data in Table 1V, it is obvious that the width of theannular space should not be more than about 5 inches nor less than about1 inch, preferably not more than 4 inches nor less than about 2 inches,for practical purposes.

For any given muiile diameter the eifect 0f increasing inutile height isto increase the production capacity of the unit., In addition to theobvious advantage ofY increasing the length of the reducing zone, anincrease in oxide feed rate is obtained which in turn requires anincreased ow of reducing gas. This results in higher reducing gasvelocities within the muflle which in turn 'improve the heat transfercharacteristics of the process. Increased height is always desirable,the only limiting factor. being practical engineering considerations, e.g., initial cost and maintenance cost of excessively high structures,etc.

The maximum particle size that can be treated successfully by thereduction operation of the present process depends mainly upon the eifective cross-sectional area of the muilie, i. e., width of oxide bed. Forany given area of mufe crosssection, the maximum permissible particlesize is that size which will moveV freely downward under the influenceof gravity without mechanical C-.lQgging Thus, for the particular muiiledimensions of furnace C described hereinbefore, -a particle size ofabout 0.75 inch is about the maximum size which can be handled withoutclogging. However, the preferred maximum particle size in this case isabout 0.5 inch since parf ticle sizes larger than about 0.5 inch` inaverage diameter require somewhat slower rates of feed than arecommercially feasible in ordertoV allow time for diffusion of thereducing gases intothe centerof each particle. Consequently, in afurnace of the size of furnace S, the reduction reac-ftion ratedecreases appreciably as the particle size increases over about 0.5inch. However, larger particle sizes can also be successfully re-y duced`provided the dimensions of the annular' muille are also increased toaccommodate these larger-sizes.

Although. the maximiun permissible particle size is controlled bythecapacity of the muiiie to handle the oxide without clogging, it has beendiscovered that the range of particle sizes of the oxide to be treatedby thepresent process is a very important factor in the successfuloperation of' the process- It has been found that if too great, aproportion ofthe oxide being treated is of' too fine a particle size,this fine fraction tends to cake or 'bridge in the reduction Inutilethus blocking the mui/lie and preventing the oxide from properly feedingthrough the muille. To obtain' the optimum rate of feed, for instance ina furnace of the dimensions of-v furnace C', it is preferred that theminimum particle size i-n the oxide feed Ybe maintained at about 0-.1inch a1- thoughv successful reduction can also be obtained with feedscontainingv oxide particle sizes down to about, 0.05 inch (about 14mesh) provided the percentage of these fine particles in the feed is nottoo high, e. g., no more than about 10% by volume of the total feed',and provided thata clean sizing separation at the particle size of about0.05 inch can be made. In order to allow for screening ineiiiciencyandvariations in particle size distribution which can occur in com-4mercial scalel operations, screening at about- 0.1 inch, e. g., fromabout 6V to about 8 U. S. standard mesh, is recommended. The preferredrange of particle size, of about 0.1 inch to about 0.5 incl-1, ascontemplatedv by the present invention for vtreatment in a mufe ofthetype of furnace C is important from the viewpoint of obtaining the bestresults. However, good results can ber obtained in larger sizecommercial equipment with wider particle size ranges, e. g., about l0.05inch to about 0.75 inch, provided that the screening facilities aresufficiently good to obtain cleanminirnum and maximum particle sizeseparations.-

'Ilhe determination of the actual particle, size rangel to be employedwith any particular size of apparatus is dictated by at least threeconsiderations. First, the dimensions and the shape of the muilie areimportant factors in determining the particle size range that may beemployed mechanical clogging and/ or caking is to be avoided. Second,ythe reduction rate decreases as the particle size increases above about0.4 to about 0.5 inch, the degree of reduction depending on the shapeand porosity` of the particles and the copper content of the oxide beingtreated. Third, the success of the present invention depends on intimatecontact of the reducing gases with the oxide particles. Conditionsfavoring intimate contact between oxide and gas are a uniformly cereus,iride bedY andv as small an oxide particle size as is consistent withporosity of the bed with out obtaining caking or bridging in the muffle.When the range of particle size of the oxide is wide, the overallporosity of the bed decreases due mainly to the fact that the finerparticles tend to segregate in the interstices between the largerparticles, thereby forming dense cakes which prevent free uniformpassage of the reducing gases. In this case, the gas will tend tochannel: throughv or around the segregated fines; and the result is. alower degreeV of reduction of the finer particle sizes as illustrated infollowing Table V, although normally it would be expected that the finersizes would experience a higher degree of reduction. Furthermore, thetendency of too fine particles to cake and sinter, thereby clogging themule tube, is a further reason why the minimum particle size isimportant and must be controlled.

For any given set of muflie dimensions having a minimum heating surfacearea to muifle volume ratio of at least about 0.4, the optimum orpermissible maximum and minimum particle size for the particular muiflemust be determined by actual test. The mufe cross-section is animportant factor and increasing the muffle crosssection, particularlywith respect to the width of the oxide bed, not only permits treatmentof finer particle sizes but also permits treatment of a largerpercentage of fine particles in comparison to the particle size rangeand minimum particle size permissible for treatment in smaller muifles.Furthermore, the permissible range and distribution of sizes determinedfor any particular apparatus also controls the percentage of fineparticles to be allowed. For instance, if the maximum allowable particlesize for a specic apparatus is determined by tests to be about 0.2 inch,the minimum permissible particle size can be as low as about 0.04 inchand the percentage of sizes between 0.04 inch and 0.1 inch can be ashigh as about 50% of the entire feed.

Another important factor in determining the permissible range anddistribution of particle sizes is the reduction temperature employed.Thus, the lower the minimum particle size and/ or the higher the percentof the finer sizes which are permissible, the lower is the reductiontemn perature which can be successfully employed. Thus, for a muflehaving the dimensions of furnace C when employing reduction temperaturesbetween about 1800 F. and aboutr2000 F., e. g., about 1900 F.; it ispreferred that the particle sizes be between about 0.05 inch and about0.5 inch with not more than about of the total feed being in theparticle size range of about 0.05 inch to about 0.1 inch.

To illustrate the effect of particle size on the degree of reduction ofboth nickel oxide (containing only about 5% copper) and nickelcopperoxide (containing about 19% copper),

each type of oxide was partially reduced in an annular mufe of thedimensions of furnace B. Four particle size ranges were screened fromsample of each type of partially-reduced oxide and the total metalcontent (percent copper plus nickel) was analyzed in each sample. Thecomparative data are given in the following Table V:

Table V Percent Copper plus Nickel in Final Product It is to be notedthat the maximum yield, measured by the total metal content, for bothtypes of oxide is obtained in the narrow particle size range of 0.263inch to 0.371 inch which lies approximately in the center of thepreferred range of about 0.1 inch to about 0.5 inch. To illustrate lethe effect of increasing the particle size range on the degree ofreduction, three tests were made on nickel-copper oxide at 1'700o F.under similar conditions of time, feed rate, and atmosphere, and in afurnace of the dimensions of furnace A. The data are given in thefollowing Table VI:

Table VI P t. 1 l C Percent a1' 1c e Size opper p us Tesi' NO Range(inch) Nickel in Final Product 15 0.051 t0 0.371 89.4 0.051 to 0.310...91.3 0.051 to 0.l25 92.1

It is apparent from the foregoing data that the more narrow the range ofparticle size, the higher is the total metal content and the greater isthe degree of reduction of the nal partially-reduced product.

In commercial operation and employing apparatus of the dimensions offurnace B, an oxide feed rate of at least about 1'75 pounds of oxide perhour, preferably about 350 pounds of oxide per hour, is desired. For amuie of the dimensions of furnace C, the desired oxide feed rate foreconomic operation is at least about 1500 pounds of oxide per hour,preferably about 3000 pounds of oxide per hour. To obtain these highfeed rates and, at the same time, to obtain a final reduced oxideproduct containing over 88%, preferably over 90%, total metal content,it has been discovered that higher temperatures in the 1500o F. to 2000F. range, preferably between about 1700o F. and l900 F., are mostbeneficial in that the rate of heat transfer is markedly increased andthe nal product, after treatment in the foregoing temperature ranges,averages between about 90% and 95% total metal content. The followingTable VII gives data illustrating the effect of Various reductiontemperatures upon the reduction of a copper-nickel oxide in a mule ofthe dimensions of furnace A, all other operating conditions beingmaintained substantially constant.

Table VII Final Prod- Test N0 Reduction Feed Rate, Gas Input, uct,Percent Temp., r. lbs/hr. Fu/lb. Cui-Percent 1, 40. 0 1. 50 82.0 1,30039. 2 l. 53 86. 3 l, 500 40. 3 l. 47 91. 6 l, 600 39. 8 1. 48 98. 2 1,700 39. 0 1. 53 93. 9 l, 800 38. 3 1. 52 94. 6 l, 900 37. 9 l. 58 95. 3

It is to be noted that at substantially the same oxide feed rate andinput rate of natural gas, there is a definite increase of total metalcontent in the partially-reduced oxide product as the temperature isincreased. An upper limit of about 2000 F. for the reduction temperatureis desirable solely from the View point of apparatus deterioration andis not restricted at this particular maximum value due to any change inthe nature of the reduction reactions causing a decrease in the totalmetal content of the treated product. It is also not desirable that thetemperature be lower than about 1500 F. purely from the viewpoint ofcommercial practicality. For instance, a rate of feed of about 35 to 45pounds of oxide per hour in a mufle of the dimensions of furnace A andselected to give about 90% to aoeaom about 92% total'V metal vcontent atabout 1500 F. does not produce anywhere near this total metal value iftreated at 1100o F. since the reduction reaction is much slower at thislow temperature. In order to obtain a satisfactory 'uniform product ofthe desired high metal content, the feed rate must be reduced to only a'fraction of the feed rate when employing temperatures above about 1500"F. The following Table VIII illustrates the feed rates necessary toobtain a satisfactory product at temperatures of 1100 F., 1300" F. and1500o F. in a muiiie of the dimensions of furnace A.

Table VIII *Data for test No. 20 is also presented in Table VII.

A most important factor affecting the production rate, i. e., the rateof feed of oxide, for any given set of operating conditions is thecopper content in the oxide being treated by the present process. Inorder to illustrate the effect of copper content in accelerating thefeed rate While obtaining satisfactory results, a series of tests weremade in a mufile of the dimensions of furnace B in which the oxidescontained both nickel and copper but wherein the copper content variedin each test from a low value of 4.8% copper to a high value of 19.2%copper. These various oxides were all reduced at l900 F. by the novelreduction operation, such as is illustrated by the flow-sheet in Fig. 5,employing the reducing equipment of the preferred design shown in Figs.

6 and '7. The optional gas recovery and recirculation system was notused in these tests.

G. 1 238 l, 900 l. 41 92. 1 11. 2 286 1, 900 1. 43 98. 0 10. 7 303 l,900 1. 58 91. 8 11. 2 310 1, 900 l. 39 92. 8 1,1. 2 331 l, 900 1. 38 91.8 19. 2 285 l, 900 1. 68 9.4. 8 10. 2 392 1, 900 1. 53 92. 2 19. 2 397l, 9U() 1. 51 91. 5 19. 2 421 l, 900l 1. 42 92. 3

spectively), the respective total metal contents show a 3.9% differencein favor of the high-copper oxide in spite of the fact that the high-copper oxide feed rate was somewhat faster. 'Ihis indication of a slowerreaction rate for the reduction of low-copper oxide as compared to theis contemplated that the partially-spent reaction rate Afor thereduction ofvr high-copper lcontent be very high, although the latter isalso very desirable. In other words, it is more important that thedegree of partial reduction be controlled to produce a consistentlyuniform metal content rather than to attempt to more completely reducethe oxide to obtain very high total metal contents. Thus, a degreey ofpartial reduction between about` and about 75% (about 90% to aboutnickel content) is much viewpoint of the commercial control of` Subsc--Yquent smelting operations than is a higher'. degree of reductionv whichvaries between about '75% and about 95% (about 92%vv to about 96%v totalcopper plus nickel) .Y The desired uniformity of produ-ct havingreductions inV the. latter higher range, e. g., from 92% to 96% copperplus nickel, can be obtained at the expense of a lowered throughputcapacity, particularly for reductions in excess of about 85% (about 94%copperplus nickel). However, it is technically possible to obtain anydesired degree of reduction with. the reduction operation and apparatus.Degrees of reduction up to about 85% or 90% are obtainable in one singlepassage of the oxide through the reduction muflie. To obtain stillhigher reductions, two or more passages of the oxide through thereduction muilie are usually re, quired. Nevertheless, for` any givenmuifle, degrees of reduction in excess of about tend to decrease thethroughput capacity more and more rapidly as the degree of reduction isine creased. Therefore, the optimum` degree of ree duction in anyparticular situation depends in large part' upon the contemplatedsubsequent processing operations and also upon the ecoa nomics of thatparticular situation.

The metal content of the raw or sintered nickel and nickel-copper oxidessuch as contemplated for treatment by the present process usually isabout '75% to about 80%, essentially all of which is combined. As theoxides are reduced, free or uncombined metal is formed in increasingamounts. However, where Values for total metal content of the nalproduct are given in the present specification, it is not meant thatthese values represent free or uncombined metal but represent free metalplus remaining combined or oxidized metal. Thus, for a reduction ofabout 75% which is equivalent to a total metal content of about 92%, thefree metal content of the final reduced product is about 69%, thebalance being combined metal.

Fig. 5 is a flow sheet illustrating the preferred overall processembodying the present invention employing countercurrent flow of naturalhydrocarbon gas to oxide to obtain a partially-reduced oxide which isthen directly smelted and refined to produce a high-grade metal product.As an embodiment of this preferred overallprocess, vit exhaust 92% totalcopper plus more desirable from the gases can be treated for theseparation of reducing components from non-reducing components in theexhaust gases, e. g., the separation of hydrogen, carbon monoxide andhydrocarbon from carbon dioxide, water vapor and possibly nitrogen. Thepartially-spent exhaust gases can be treated for recovery of hydrogen,carbon monoxide, hydrocarbons, carbon dioxide, etc., in a recoverysystem such as indicated within the area bounded by dotted lines in thenow-sheet shown in Fig. 5. From a commercial viewpoint, recoveredreducing gases, e. g., carbon monoxide, hydrogen and hydrocarbon gases,can be utilized in various ways, for instance, as reducing atmospheresin heat treating furnaces or, preferably, as a supplementary supply ofreducing gas for the present process. In addition, carbon dioxide can berecovered as a commercial byproduct.

For instance, Fig. shows that the partiallyspent exhaust gases are drawnby means of a suitable pump through conduit 32 into a condenser33 toremove the bulk of the Water vapor. The gases from the pump outlet nowcontaining hydrogen, carbon monoxide, hydrocarbons, carbon dioxide, andinert gases (mainly nitrogen) continue into the bottom of a carbondioxide absorbing unit 34 of commercial design utilizing aqueousmonoethanolamine solution as the absorbing agent. The carbon dioxide onpassing upward through the absorbing unit with the reducing gases isremoved by the downward-moving cold amine solution. The cold aminesolution on leaving the bottom of the absorbing unit with its burden ofcarbon dioxide passes through a heat exchanger 35 to partially coolcarbon dioxide-free amine solution that is then introduced at the top ofthe absorber unit. The carbon dioxide-containing amine solution leavingthe unit is thereby preheated before its entry into the top of the aminesolution reactivator 36. Heat introduced into this unit causes the aminesolution to release the carbon dioxide which passes upward through aWater cooler where vaporized and entrained amine solution is condensedand returned to the reactivator. Recovered carbon dioxide is withdrawnfrom the cooler as a valuable by-product. The hot amine solution, nowfree from carbondioxide, is drawn off at the bottom of the reactivatorby a pump and passed through the heat exchanger 35 where it is partiallycooled, thereby heating the out-going carbon dioxide-containing aminesolution from the absorber. The partially-cooled, carbon dioxide-freeamine solution continues on from the heat exchanger to a water cooler 31where it is cooled to the proper' temperature for absorbing carbondioxide and then returned to the absorber thus completing the absorptioncycle. Reducing gases coming off the top I" the absorber 34 containhydrogen, carbon monoxide, hydrocarbons, and a small amount of inertgases, such as nitrogen, but are essentially free from carbon dioxideand water vapor. These reducing gases are available for reintroductioninto the reduction mule together with raw natural gas. Thus, the highconcentrations of reducing components in the gas necessary to obtainmaximum reduction of oxide at a rapid rate can be obtained with aminimum consumption of raw gas. The feed rate of oxide or, in otherwords, the furnace throughput capacity can thereby be markedlyincreased; `'and the heat requirements per unit weight of oxide reducedare considerably lowered since heat units, which other- Wise. would benecessary to decompose large excesses of raw gas, are utilized insteadfor heating the oxide to the required reducing temperature.

By recovering` and re-circulating unoxidized combustibles andhydrocarbons contained in the partially-spent exhaust gas, more completeuti-- lization is made of the total reducing potential present in theoriginal raw gas and, as a result, the actual amount of gas consumed perunit Weight of oxide reduced more closely approaches. the ideal ortheoretical oxidation-reduction ratioof about one cubic foot of WestVirginia natural gas per pound of oxide. In this manner, for any givenfeed rate, the percentV total metal con-v tent obtained in the finalreduced product is increased; and the consumption of gas per pound ofoxide thus reduced is substantially lowered. The benefits derived fromtreating partiallyspent exhaust gases to recover therefrom the activereducing components and re-circulating said recovered reducingcomponents back through the reduction muflle are illustrated by the datapresented in the following Table X. The data for test Nos. 44 to 48,inclusive, were obtained by re-circulating recovered reducing gases andthe data for test Nos. 39 to 43, inclusive, were obtained by employing alarge excess of raw natural gas only, e. g., 50% excess, to supply theconcentration of reducing components necessary to obtain the requireddegree of reduction. The results shown in Table X were obtained infurnace A, the temperature being maintained in all cases at about 1800F.

liti. D.=Not determined. l:Balance of 1re-circulated gas mainlyhydrocarbons.

From an analysis of Table X, it can be seen that re-circulation ofrecovered reducing gases increases the degree of reduction obtained oralternatively, increases the production or throughinert gases, such asnitrogen, presentA in the raw natural gas used for reduction. Thequantity of valuable reducing components `lostin this escaping gas islargely determined by the quantity of natural gas introduced into themule and the degree of reduction obtained. For example, on theassumption that r% reduction is required, this theoretically wouldrequire about 0.75 cubic foot of gas per pound of oxide feed. Therefore,if

2l 75% reduction is attained, any natural .gas indeduced inte 'the faunein excess of abeut offs :cubic 'foot per pound of oxide feed can beexhausted through the charging ein in the form f partially-'spentreducing gases. 'The amount cf excess natural gas introduced into thernuie is 'an `amount su'cie'nt only to prevent excessive build-up Vofinert gases in the recovered and re- 'circulate'd reducing gases.Several methods exist of controlling bleeding of partially-spent exhaustgas through the charging bin to .prevent excess build-up of the inertgas components in lthe munie. The preferred method is the 'onehereinbefore described and is preferred largely on the 'basis of thesimplicity 'of control 'which itprvides Increasing the input of naturalgas above the theoretical value serves to increase considerably the heatrequirements for the system, the excess heat being utilized primarilyfor 'decomposing th excess hydrocarbon gas Iwhich is exhausted ron themui'e before its reducing potential has been profitably used.ThereforeLfor most economical production on a commercial scale, recoveryand re-use of these reducing components in the par,- tially-spentexhaust gas is 'a desirable, although not an essential, feature of thepresent in vention, as shown by the data in the foregoing Table This isespecially true where an outlet exists for the sale of the carbondioxide recovered as ley-product.

Figs. 6 and 7 are sectional elevational views of a preferred structure'of the novel, annular, oxidereduction munie of the present invention. In'ore der to obtain the `high degree of operating efficiency whereby highconcentrations of uncon-` taminated reducing gases together with excel--lent heat-transfer characteristics are econonii'- cally obtained, it isnecessary to employ the present novel structure ofereduction inutile. vApreferred embodiment of the complete assembly of novel annular reductionmunie is illus= trated in Fig. 6'. The core-heating chamber, flame tubeand annular oxide-reduction chainber portions of theannular munie areshown in detail in Fig. 7. This 'novel structure is necessary to preventexcessive lowering of thermal efficiency when munie diameters exceedabout 5 inches. The example of the novel munie Vstructure illus-- tratedin the aforementioned figuresl involves supplying heat to the core ofthe downward moving annular column of oxide as well as to the outside ofsaid annular column of oxide. This is accomplished by providing anannular oxideieduction chamber 20 (Fig. 7) for the downward passage ofthe oxide. The inside wall of the annular oxide-reducing chamber iscommon to the wall of the interior, closed-end, ccire-lieat= ing chamber2l (Fig. '7) the heat being provided, for instance, either by asemi-long-lame burner or by a partial-premix burner inserted vthereinand comprising name tube 'A2 (Fig. 7) and flame-- retention tip 23 (Fig.7). However,- any typehof burner may be usedprovided it satisfies therequrement of even, controlled distribution of heat. The outside wall ofsaid annular oxide-reducing chamber is common to the interior wall ofthe exterior combustion muflle 24 (Fig. 6) to which heat is suppliedpreferably by tangentially=firing gas burners 25 (Fig. e arrangedsph-any relative to one another. l

Control of the rate of combustion of the heat/'j ing gases applied bothexternally and internally to the annular oxide-reducing chamber iseffect; ed by means known to those skilled in the art. Although heat canbe supplied to the outside wall and to the core of the annular reductionchamber fromelectrlc-power seurce's. e.. g., electricheating elements;r'tlispreferable-that'the source of:` heat. be; obtained by thelcombustion of gas, oil or powderedfuelamore preferably by the combustionof the same-.natural gas which is introduced. into the annularreductionr chamber.. Except inavery few areas where electric power isvery cheap in comparison to the cost ofA gas, oil` or c oal, electricpower is the least desirable source of heat for the oxide-reductionoperation. A` very important factor favoring employment of natural gas,.oill and powdered` coal as the source of heat is that the atmosphereproduced. by the combustin of these fuels", particularly natural gas,`c'a'n be easily controlledy tocontain essentially no free oxygen, i'.e., can be controlled to produce neutral to reducing" atinospheresl Thisis' of great importance i-n p'i'olori'girigy the service life ofmetallic nufiles", particularly when operated at t'eiiiperatV `es` aboveabout 1500" Fl The muflle is' preferably constructed of heat-resistantmetal, more prefer-ab y a ickeI-chr'ome-iron alloy sold under thetrade-niark Iric'onel."

After passage through the reducing chamber. th'rdced Xld' is; Cooled tat least below its reoxidatiori temperature in air, e. g., to at leastabout 550' Fi Where the flow of gas is countercurrent to the movement'of oxide, this cooling Of tl reduced X'ld t abt 55.0 F. O1* lOWel iseffected by the incoming, cold, raw, natural gas'v and also by water-ldchamber 26 (Fig. 6)

from whenceeit is discharged via a novel discharging nichanisi 2T to bin23 (Fig'. 6). Where the flow of gasis concurrent with `the movement ofoxide, the cooling o f the reduced oxide is almost solely effected byefficient heat transfer between water-cooled chamber 2G and the reducedoxide. Discharge mechanism 21 is the only continuously moving mechanicalpart in the entire novel reductiony apparatus. This mechanisxn serves toregulate the rate of feed of the material through the apparatus but isnot a gas-'tight seal. In effect, the column of reduced oxide rests on ashelf or table within the discharger housing. The discharger blade,located well below the end of the munie water jacket 25,

gently pushes the reduced oxide off the shelf by a slow reciprocatingmotion. Since there is adequate space between the table-bladecombination and the end of the munie waterjacket, there is no shearingof the ductile, reduced product; and cc )nsequentlyi wear of the movingblade is negligible. In other words, since this mechanism comes intocontact'only with reduced oxide of high metal content and not withunreduced oxide,

it is not subjected to extremely high abrasive action of unreduced rawoxides. Furthermore, the carbon deposited on and within the reducedoxide particles servesl as an excellent lubricant for the movement ofboth' the blade and the reduced oxide across the surface of the table.As a result, this mechanism is relatively troublefree in operation andhas an unusually long serviceY life.

The exact maximum temperature to which the reduced oxide must be cooledis influenced by the degree of activity of the reduced oxide; Thegastight seals 29 and 3G (Fig.` e) at the receiving and dischargingports of bin 2B', respectively, are so arranged that when one seal isopen, the other is closed, thereby substantially excluding dilutingand/or oxidizing agents, such as air, from thc munie; In employingcounter-current now of gas to oxide, the gas is introduced` into themunie through gas-inlet port 3| (Fig. (i).

In the presentspecication, wherel any total metal content values (percent copper plus nickel) are given, these values represent analysesmade. on a carbon-free basis. Also, where the termv nickel-copper oxideis employed, it is meant. that said oxide is mainly a mixture of copperand nickel oxides although it is possible that; compounds of copperoxide and nickel oxide, together with some iron oxide, silica, etc.,might also be present.

It is to be observed that the present invention. provides a novelprocess for producing metal from raw oxides, particularlynickel-containing oxides, which comprises reducing raw oxides ofcontrolled particle size with hydrocarbon gases,l particularly methane,to provide reduced oxide products having consistently uniform and hightotal metal contents and controllable, consistently uniform contents ofhighly-active carbon nely dispersed throughout Vthe reduced oxideparticles and then directly smelting and refining said reduced oxideswithout substantial additions of supplementary reducing agents. Theforegoing novel process, when employed in the production of metal fromraw oxides of said metal, results in the elimination of Variouscomplicated, expensive, timeand space-consuming operations necessarywhen producing metal from raw oxides by prior art methods and providesreduced oxides which are directly converted to metal by electric-- areor induction-furnace practice.

Furthermore, the invention provides a novel unitary reduction apparatuswhich combines the characteristics of excellent heat transfer betweenheat source, gases and oxide and high concentrations oiuncontaminatedreducing gases in contact with the oxides.

Moreover, the present invention provides a new product, heretoforeunobtainable by conventional processes, which is a partially-reducedmetallic oxide having a consistently high and uniform metal content andhaving a controlled, uniform, highly-active carbon content nelydispersed throughout the reduced oxide particles.

Although the present invention has been described in conjunction withcertain preferred embodiments, it is to be understood that modicationsand variations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Thus, metallic oxides having oxygen dissociation pressurescomparable to those of nickel oxide and copper oxide, including theoxides of lead, bismuth, cobalt, etc., can also be reduced by thepresent process regardless of whether or not nickel oxide and/or copperoxides are also present. However, cobalt oxide is the oxide most likelyto be associated with nickel oxide and/or copper oxide and the presentinvention is particularly applicable to the treatment of the oxides ofthe metals cobalt, nickel and copper which have the atomic numbers 2'7,28 and 29, respectively. Such variations and modiiications are to beconsidered within the purview of the application and the scope of theappended claims.

.We claim:

1. A process for controlled reduction of oxides of metal having atomicnumbers from 27 to 29 to obtain partially-reduced oxide ofconsistentlyuniform, high, total metal content and containing controlledamounts of uniformly dispersed, finely-divided, highly-active carbon andcapable of being directly converted into high-quality metal withoutsubstantial additions of supple- 24 mentary reducing agents whichcomprises establishing a substantially vertical annular column of atleast one of said oxides having a particle size between about 0.1 inchand about 0.5 inch, said column having an effective width between about2 inches and about 4 inches and having a ratio of surface area to volumeof at least about 0.5; heating said oxide in a single operation to atemperature between about 1700 F. and about 1900 F. out of contact withcombustion gases and in contact with countercurrently flowinghydrocarbon gas containing about 75% to about methane to obtaincontrolled partial reduction of said oxide to a uniform total metalcontent between about 88% and about 95% and to obtain controlledvuniform dispersion of about 0.4% to about 4.0% finely-divided,highly-active carbon within the particles of partially reduced oxide;and cooling said oxide in a non-oxidizing atmosphere to a temperaturebelow at least about 550 F.

2. A process for controlled reduction of oxides of metal having atomicnumbers from 27 to 29 to obtain partially-reduced oxide ofconsistentlyuniform, high, total metal content and containing controlledamounts of uniformly-dispersed, finely-divided, highly-active carbon andcapable of being directly converted into high-quality metal withoutsubstantial additions of supplementary reducing agents which comprisesestablishing a substantially vertical annular column of at least one ofsaid oxides having a particle size between about 0.04 inch and about0.75 inch, said column having an effective width between about 1 inchand about 5 inches and having a ratio of surface area to volume of atleast about 0.4; heating said oxide in a single operation to atemperature between about '1500 F. and about 2000 F. out of contact withcombustion gases and in contact with countercurrently flowinghydrocarbon gas to obtain controlled partial reduction of said oxide toa uniform total metal content of at least about 88% and to obtaincontrolled uniform dispersion of about 0.4% to about 4% finely-divided,highly-active carbon within the particles of the partially-reducedoxide; and cooling said oxide in a non-oxidizing atmosphere to atemperature below at least about 550 F.

3. A process for controlled reduction of oxides of metal having atomicnumbers from 27 to 29 to obtain partially-reduced oxide ofconsistentlyuniform, high, total metal content and containing controlledamounts of uniformly-dispersed, nely-divided, highly-active carbon andcapable of being directly converted into high-quality metal withoutsubstantial additions of supplementary reducing agents which comprisesestablishing a substantially vertical annular column of at least one ofsaid oxides having a particle size between about 0.1 inch and about 0.5inch, said column having an effective width between about 2 inches andabout 4 inches and having a ratio of surface area to volume of at leastabout 0.5; heating said oxide in a single operation to a temperaturebetween about 1700 F. and about 1900 F. out of contact with combustiongases and in contact with concurrently flowing hydrocarbon gascontaining about 75% to about 95% methane to obtain controlled partialreduction of said oxide to a uniform total metal content of about 88% toabout 95% and to obtain controlled uniform dispersion of about 0.05% toabout 0.6% finely-divided, highly-active carbon within the particles ofthe partially-reduced oxide; and

25` cooling said oxide in a nonexidizifig atiisphere to a temperaturebelow` atleast about 550 F. Y

. 4.,A process for Acontrolled reduction ofoxides of metal having.atomic numbers from 27 to 29 to obtain partially-reduced oxide ofconsistentlyuniform, high. total metal content andcontaining controlledamounts of uniformly-dispersed, finely-divides, mercy-activ 'carbn andcapable of being directly converted into high-quality metal withoutsubstantial additions of supplementary reducing agents which comprisesestablishing a substantially vertical annular column of at least one ofsaid oxides having a particle size between about 0.04 inch and about0.75 inch, said column having an effective width between about 1 inchand about 5 inches and having a ratio of surface area to volume of atleast about 0.4; heating said oxide in a single operation to atemperature between about 1500 F. and about 2000 F. out of contact withcombustion gases and in contact with concurrently flowing hydrocarbongas to obtain controlled partial reduction of said oxide to a uniformtotal metal content of at least about 88% and to obtain controlleduniform dispersion of about 0.05% to about 0.6% finely-divided,highly-active carbon within the particles of the partially-reducedoxide; and cooling said oxide in a non-oxidizing atmosphere to atemperature below at least about 550 F.

5. A process for controlled reduction of oxides of metal having atomicnumbers from 27 to 29 to obtain partially-reduced oxide ofconsistentlyuniform, high, total metal content and containing controlledamounts of uniformly-dispersed, finely-divided, highly-active carbon andcapable of being directly converted into high-quality metal withoutsubstantial additions of supplementary reducing agents which comprisesestablishing a substantially vertical annular column of at least one ofsaid oxides having a particle size between about 0.04 inch and about0.75 inch, said column having an effective width between about 1 inchand about 5 inches and having a ratio of surface area to volume of atleast about 0.4; heating said oxide in a single operation to atemperature between about 1500 F. and about 2000" F. out of contact withcombustion gases and in contact with flowing hydrocarbon gas to obtaincontrolled partial reduction of said oxide to a uniform total metalcontent of at least about 88% and to obtain controlled uniformdispersion of about 0.05% to about 4.0% finely-divided, highly-activecarbon within the particles of the partially-reduced oxide; and coolingsaid oxide in a non-oxidizing atmosphere to a temperature below at leastabout 550 F.

6. As a new article of manufacture, a partiallyreduced particle of oxideof metal having atomic numbers from 27 to 29, said particle having asize of about 0.1 inch to about 0.5 inch and containing a total metalcontent of about 88% to about 95% together with about 0.4% to about 4.0%highly-active, finely-divided carbon uniformly dispersed within saidpartially-reduced particle.

7. As a new article of manufacture, a partiallyreduced particle of oxideof metal having atomic numbers from 27 to 29, said particle having asize of about 0.1 inch to about 0.5 inch and containing a total metalcontent of about 88% to about 95% together with about 0.05% to about0.6% highly-active, finely-divided carbon uniformly dispersed withinsaid partially-reduced particle.

8. As a new article of manufacture, a partiallyaccessi Cil' reducedparticle ofxid ofirfietal having atomic numbers from, 2,7 to29,saidp'article having a size of 'about004uinch `to about 0.75 inch andcontaining a total nmetal content of at least about 88% r togetherwithabout 0.05% .to a\bout.4.0% highly-active; hely-divid'ed carbonuniformly dispersed Awithin `'said .partially-reduced particle.

9. Asa new article of manufacture, a partiallyreduced particle of oxideof'metal having atomic numbers from '27156 29, said particle having asize of about 0.04 inch to about 0.75 inch and containing a total metalcontent of at least about 58% together with about 0.4% to about 4.0%highly-active, finely-divided vcarbon uniformly dispersed within saidpartially-reduced particle.

l0. As a new article of manufacture, a partially-reduced particle of anickel-containing oxide, said particle having a size of about 0.04 inchto about 0.75 inch and containing a total metal content of at leastabout 88% together with about 0.4% to about 4.0% highly-active,nely-divided carbon uniformly dispersed within said partially-reducedparticle.

1l. A process for controlled reduction of a nickel-containing oxide toobtain partially-reduced oXide of consistently-uniform, high, totalmetal content and containing controlled amounts of uniformly dispersed,nely-divided, highlyactive carbon and capable of being directlyconverted into high-quality metal without substantial additions ofsupplementary reducing agents which comprises establishing asubstantially vertical annular column of said oxide having a particlesize between about 0.1 inch and about 0.5 inch, said column having aneffective width between about 2 inches and about 4 inches and having aratio of surface area to volume of at least about 0.5; heating saidoxide in a single operation to a temperature between about 1700 F. andabout 1900 F. out of contact with combustion gases and in contact withcounter-currently ilowing hydrocarbon gas containing about 75% to aboutmethane to obtain controlled partial reduction of said oxide to auniform total metal content between about 88% and about 95% and toobtain controlled uniform dispersion of about 0.4% to about 4.0%finely-divided, highly-active carbon within the particles of partiallyreduced oxide; and cooling said oxide in a non-oxidizing atmosphere to atemperature below at least about 550 F.

12. A process for controlled reduction of a nickel-containing oxide toobtain partiallyreduced oxide of consistently-uniform, high, total metalcontent and containing controlled amounts of uniformly-dispersed,finely-divided, highly-active carbon and capable of being directlyconverted into high-quality metal without substantial additions ofsupplementary reducing agents which comprises establishing asubstantially vertical annular column of said oxide having a particlesize between about 0.04 inch and about 0.75 inch, said column having aneffective width between about 1 inch and about 5 inches and having aratio of surface area to volume of at least about 0.4; heating saidoxide in a single operation to a temperature between about 1500 F. andabout 2000 F. out of contact with comb-ustion gases and in contact withcountercurrently flowing hydrocarbon gas to obtain controlled partialreduction of said oxide to a uniform total metal content of at leastabout 88% and to obtain controlled uniform dispersion of finely-divided,highly-active carbon within the particles of the partially-reducedoxide; and

. 27 28 ooling said oxide in a, rich-oxidizing atmosphere Number NameDat to a. temperature below at least about 550 F. 1,480,212 Lamothe Jan.8, 1924 HARRY E. TSCHOP. 1,550,271 Macklind et al Aug. 18,' 1925 J QSEEHEDWIN CARTER. 1,848,710 Gustafsson Mar. 8, 1932 CHARLES BRUCE GOODRICH.5 2,166,207 Clark July 18, 1939 2,256,536 Udy Sept. 23, 1941 RferencesCited in the le of this patent 2,296,841 Y Gardner Sept. 29, 1942 UNITEDSTATES PATENTS 2,302,615 LIIZ NOV. 17, 1942 2,417,949 Riveroll Mar. 25,1947 Number Name Date 1,075,135 Alton oct. '1, 1913 1-

5. A PROCESS FOR CONTROLLED REDUCTION OF OXIDES OF METAL HAVING ATOMICNUMBERS FROM 27 TO 29 TO OBTAIN PARTIALLY-REDUCED OXIDE OFCONSISTENTLYUNIFORM, HIGH, TOTAL METAL CONTENT AND CONTAINING CONTROLLEDAMOUNTS OF UNIFORMLY-DISPERSED, FINELY-DIVIDED, HIGHLY-ACTIVE CARBON ANDCAPABLE OF BEING DIRECTLY CONVERTED INTO HIGH-QUALITY METAL WITHOUTSUBSTANTIALLY ADDITIONS OF SUPPLEMENTARY REDUCING AGENTS WHICH COMPRISESESTABLISHING A SUBSTANTIALLY VERTICAL ANNULAR COLUMN OF AT LEAST ONE OFSAID OXIDES HAVING A PARTICLE SIZE BETWEEN ABOUT 0.04 INCH AND ABOUT0.75 INCH, SAID COLUMN HAVING AN EFFECTIVE WIDTH BETWEEN ABOUT 1 INCHAND ABOUT 5 INCHES AND HAVING A RATIO OF SURFACE AREA TO VOLUME OF ATLEAST ABOUT 0.4; HEATING SAID OXIDE IN A SINGLE OPERATION TO ATEMPERATURE BETWEEN ABOUT 1500* F. AND ABOUT 2000* F. OUT OF CONTACTWITH COMBUSTION GASES AND IN CONTACT WITH FLOWING HYDROCARBON GAS TOOBTAIN CONTROLLED PARTIAL REDUCTION OF SAID OXIDE TO A UNIFORM TOTALMETAL CONTENT OF AT LEAST ABOUT 88% AND TO OBTAIN CONTROLLED INIFORMDISPERSION OF ABOUT 0.05% TO ABOUT 4.0% FINELY-DIVIDED, HIGHLY-ACTIVECARBON WITHIN THE PARTICLES OF THE PARTIALLY-REDUCED OXIDE; AND COOLINGSAID OXIDE IN A NON-OXIDIZING ATMOSPHERE TO A TEMPERATURE BELOW AT LEASTABOUT 550* F.
 8. AS A NEW ARTICLE OF MANUFACTURE, A PARTIALLYREDUCEDPARTICLE OF OXIDE OF METAL HAVING ATOMIC NUMBERS FROM 27 TO 29, SAIDPARTICLE HAVING A SIZE OF ABOUT 0.04 INCH TO ABOUT 0.75 INCH ANDCONTAINING A TOTAL METAL CONTENT OF AT LEAST ABOUT 88% TOGETHER WITHABOUT 0.50% TO ABOUT 4.0% HIGHLY-ACTIVE, FINELY-DIVIDED CARBON UNIFORMLYDISPERSED WITHIN SAID PARTIALLY-REDUCED PARTICLE.